A rotating electric machine such as a motor, a generator, or the like includes a permanent magnet type synchronous rotating machine having a permanent magnet in its rotor.
Japanese Patent Laying-Open No. 2000-037053 discloses a rotating electric machine including a stator having a stator coil, a rotor constituted by a permanent magnet for forming a magnetic pole mounted into a through-hole provided in a rotor core, and a rotation shaft pressed into the rotor core.
One of the embodiments of the document has a description that an adhesive is applied to a non-magnetic end plate to be pressed into the rotation shaft, on the side of the rotor core, to reliably prevent the end plate and the permanent magnet from being pulled out during high-speed rotation.
However, when the non-magnetic end plate is directly bonded to the rotor core, the core portion bears a burden when the rotating electric machine is subjected to repeated thermal cycles of heating and cooling, due to the difference in linear expansion coefficients of the materials of the two components.
FIG. 10 is a view for illustrating a shape of a magnetic steel plate 52 used as a rotor core.
Referring to FIG. 10, magnetic steel plate 52 is an annular steel plate having a hole in its central portion, and the hole portion in the central portion has projections 111 and 112 fitting to a shaft for positioning. Further, the peripheral portion has holes 101 and 102 for inserting permanent magnets.
Such magnetic steel plates 52 are stacked to form a rotor core.
FIG. 11 is a view for illustrating a section of a rotor corresponding to the portion XI-XI in FIG. 10.
Referring to FIG. 11, a plurality of magnetic steel plates 52 are stacked over an end plate 41. Each of holes 101 and 102 in magnetic steel plate 52 in FIG. 10 forms a through-hole for inserting a permanent magnet 56 in the core. An adhesive 54 is injected into the through-hole, permanent magnet 56 is inserted, and finally an end plate 40 is mounted onto the core. On this occasion, adhesive 54 may enter a gap between end plates 40 and 41 and the rotor core, and bond the magnetic steel plates at the ends of the rotor core to end plates 40 and 41.
FIG. 12 is a view for illustrating stress imposed between the end plate and the magnetic steel plate.
Referring to FIG. 12, suppose that end plate 40 and magnetic steel plate 52 are partly bonded with adhesive 54. For example, in FIG. 10, there may be a case where a portion on the periphery of holes 101 and 102 is partially bonded to end plate 40 with an adhesive.
Typically, end plate 40 is made of an aluminum alloy, and as shown in FIG. 12, an amount of thermal expansion and thermal shrinkage D40 of an aluminum alloy is greater than an amount of thermal expansion and thermal shrinkage D52 of magnetic steel plate 52.
When end plate 40 and magnetic steel plate 52 have significantly different linear expansion coefficients, magnetic steel plate 52, which is thinner and disadvantageous in terms of shape, is subjected to excessive stress due to repeated heating and cooling. In particular, a region 103 in FIG. 10 is thinner because holes 101 and 102 are provided therein. When magnetic steel plate 52 in the vicinity of holes 101 and 102 is bonded to end plate 40 with the adhesive, stress due to the difference in linear expansion coefficients is concentrated in region 103. If such stress is repeatedly imposed, fatigue breakdown of the magnetic steel plate may occur.